1. Field of the Invention
This invention relates to variable reluctance motor systems.
2. Description of Related Art
A single phase variable reluctance motor system typically comprises a stator having a pair of oppositely disposed salient poles provided with energising windings, a rotor having a pair of oppositely disposed salient poles without windings, and a control circuit for rotating the rotor by supplying current pulses to the stator windings in synchronism with rotation of the rotor. Such a motor system offers the advantage, over a conventional motor system having rotor windings, that commutator brushes, which are wearing parts, are not required for supply of current to the rotor. Furthermore significant advantages over other motor systems are provided by the fact that there are no conductors on the rotor, and high-permanence magnets are not used in the motor construction.
However, although they are simple in construction, conventional single phase variable reluctance motor systems suffer from the fact that they are non-self-starting since it is inherent in their construction that positive torque is available for only 180.degree. at most per 360.degree. cycle, and there are large zones (of about 90.degree.) intermediate the stator poles where positive torque is not available so that, if the rotor has stopped with its poles orientated in these zones, the motor system cannot be re-started without first having to turn the rotor to a position in which torque becomes available. This rules out such single phase variable reluctance motor systems for certain applications and in particular for driving difficult loads such as those which combine direct drive and high friction, for instance.